1. Field of the Invention
This invention relates to electronics technology, and, more particularly, to a digitally-controlled pyroelectric signal sampling circuit designed for use to process the alternating current (AC) pyroelectric signal generated by a pyroelectric device, such as a pyroelectric infrared sensor, such that the AC signal is converted into direct current (DC) signal.
2. Description of Related Art
A pyroelectric infrared sensor is an infrared-sensitive electronic device capable of generating analog electric signals in response to temperature changes in the ambient environment. Owing to this characteristic, pyroelectric infrared sensors are widely utilized as a key component in temperature detectors, achromatic infrared gas analyzers and devices for detecting carbon dioxide or carbon monoxide concentrations, to name just a few.
Conventional pyroelectric infrared sensors, however, are irresponsive to DC inputs, and, therefore, when the input signal is a DC type, it is necessary to convert the DC input into AC in order to allow the DC input to be detected by the pyroelectric infrared sensor, and then convert the AC output of the pyroelectric infrared sensor to DC in order to allow a DC output signal to be used to indicate the condition at the input end.
A solution to the foregoing problem is to utilize filters or rectifiers to convert the AC output of the pyroelectric infrared sensor into DC. However, one drawback of this solution is that it requires quite a lengthy period of time before the DC output reaches its steady state, and, therefore, it doesn't allow the output to instantaneously reflect information about the condition at the input in real time. A conventional solution to this problem has been disclosed in ROC Patent No. 127857, which is characterized by the use of a subtraction operation on the upper peak and the bottom peak in the waveform of the AC output to thereby obtain a DC output. This helps to allow the output to instantaneously reflect information about the condition at the input in real time.
One drawback to the ROC Patent No. 127857, however, is that its operating characteristics are affected by temperature changes in the ambient environment, thus undesirably resulting in inaccurate output-to-input characteristic. This problem is due to the use of an analog-type time delay and sampling circuitry to perform the subtraction operation on the upper peak and the bottom peak of the AC output, and analog-type circuitry is quite susceptible to temperature changes.